Vertical Transmission Structure

ABSTRACT

A vertical transmission structure for high frequency transmission lines includes a conductive axial core and a conductive structure surrounding the conductive axial core. The vertical transmission structure is applied to a high-frequency flip chip package for reducing the possibility of underfill from coming in contact with the conductive axial core.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to vertical transmission structures, andvertical transmission structures for high-frequency transmission lines.

2. Background of the Related Art

Along with the rapid advances in wireless communication productsdevelopment in recent years, a planar PCB architecture can not satisfythe demand of low cost, high density and compact products. Thus, thevertical interconnection of low temperature co-fired ceramics (LTCC)package or multi-layer PCB have gradually replaced the design of theplanar PCB. However, the via design for the multi-layer PCB or LTTC maycause parasitic impedances or inductances.

There have been various types for vertical transmission, such astransmission between microstrip line and strip line, microstrips,coplanar waveguides, or coplanar waveguide and strip line. Taking thefirst type as an example, the vertical transmission interconnectsbetween the coplanar waveguides do not cause large return loss in lowfrequencies, however, the parasitic effects from the verticaltransmission interconnects can degrade the characteristics of returnparameters with increase in the operating frequencies. Generally, thecompensation of local matching may reduce the parasitic effects andfurther convert them to inductance effect to achieve both the impedancematch and prevent the parasitic effects. In the second type, themicrostrip line transmission with slots or cavities does not adopt a viaarchitecture to prevent the parasitic effects. The slot configurationmay generate inductance effects to achieve impedance match. The improvedcavity configuration includes both a dielectric layer between two groundlayers made of same metallic material and a slot to perform coupling bywaveguides. In the third type, the transmission between microstrip lineand strip line improves frequency band characteristics by high impedancecompensation that utilizes a high-impedance line with additionalinductance to compensate the capacitance of transmission lines. It maybe due to different impedances generated by the lines with variouswidths. The impedances may be raised by decreasing the widths andconverted into inductances.

FIG. 1 is a top-view perspective diagram illustrating a conventionalthree ground bump configuration of a high-frequency flip chip package. Asubstrate 10 has a coplanar waveguide 12. The circuit layer 16 of amicrowave chip package 18 is coupled to the coplanar waveguide 12 viathree bumps 14. There are various transmission structures applied tovarious packages. Basically, the parasitic effects from various wiringconfigurations of the packages are raised with increase of operatingfrequencies. Thus, flip chip package has been gradually applied tohigh-frequency products. However, when the underfill comes in contactwith the transmission structures of the flip chip package, significantwaveband frequency loss of transmission lines occurs. Attempts are stillbeing made to improve the transmission architecture of transmissionlines to achieve reduction in the loss of waveband frequency.

SUMMARY OF THE INVENTION

The present invention is directed to a transmission structure, which maybe suitable for reducing the possibility of the underfill from coming incontact with the vertical transmission structure between connected linesto increase the performance of the transmission lines.

The present invention is also directed to a transmission structure whichmay be suitable for improving the transmission efficiency between amicrowave chip and a package substrate and reduce crosstalk insertionloss and return loss of the signal lines.

The present invention is also directed to a transmission structurehaving a coaxial configuration suitable to provide more return currentpaths.

Accordingly, one embodiment of the transmission structure of chipincludes a chip having an insulating surface; a signal line disposedover the insulating surface, wherein the signal line includes a bar bumpand two terminals; a ground bump separately disposed over insulatingsurface and electrically isolated from the signal portion line, and anexpansion bump formed around each terminal; a dielectric layer disposedover the signal line and the ground bump, wherein the dielectric layerexposes the two terminals and a portion of each expansion bump; twofirst conductive connectors disposed over the dielectric layer, whereinthe two first conductive connectors respectively correspond and incontact with the two exposed expansion bumps; and two second conductiveconnectors disposed over the dielectric layer and respectively incontact with the two exposed terminals, wherein each of the secondconductive connectors respectively serve as a centre of the firstconductive connectors.

Another embodiment of the transmission structure of high-frequencytransmission line includes a substrate having an insulating surfaceformed thereon; a pattern of high-frequency transmission structuresdisposed over the insulating surface, wherein the pattern ofhigh-frequency transmission structures includes a signal line having abar bump and a terminal; and a ground bump separately set over thesubstrate and electrically isolated from the signal line, wherein theground bump surrounds the bar bump and includes an expansion bumpsurrounding the terminal; a dielectric layer disposed over the patternof high-frequency transmission structures, wherein the dielectric layerexposes the terminal and the expansion bump of the ground bump; a firstconductive connector disposed over the dielectric layer and in contactwith the exposed expansion bump; and a second conductive connectordisposed over the dielectric layer and in contact with the exposedterminal, wherein the second conductive connector serves as a centre ofaxis of the first conductive connector.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top-view perspective diagram illustrating a conventionalthree-grounding bump of a high-frequency flip chip package.

FIGS. 2A to 2E are cross-sectional perspective diagrams illustrating aprocess of fabricating substrates of high-frequency flip chip packageaccording to one embodiment of the present invention.

FIG. 3A is a top-view perspective diagram illustrating a high-frequencyflip chip package according to one embodiment of the present invention.

FIG. 3B is a scaled-up schematic diagram illustrating a transmissionstructure according to one embodiment of the present invention.

FIG. 4 is a schematic diagram illustrating the combination of asubstrate and package according to one embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 2A to 2E are cross-sectional perspective diagrams illustrating aprocess of fabricating substrates of high-frequency flip chip packageaccording to one embodiment of the present invention. As shown in FIG.2A, a conductive layer is formed over a substrate 11 having aninsulating surface. A pattern of high-frequency transmission structuresis transferred onto the conductive layer. The pattern of high-frequencytransmission structures includes a signal line 15 and a ground bump 13electrically isolated from each other. In one embodiment, the substrate11 may be comprised of a single or multiple layers made of glass,silicon, ceramic or polymer material. The conductive layer may include acopper foil laminated with the substrate 11, a copper foil withelectroplated copper, or a substrate electroplated with an electroplatedcopper. Alternatively, the conductive layer may include, for example butnot limited to, a gold layer, and may be formed over the substrate 11 bylithography and electroplating process.

Next, the signal line 15 extends from one side of the substrate 11 tothe centre thereof, and comprises a bar bump and a terminal 151. Theground bump 13 extends from the side of the substrate 11, and includes akey hole shaped opening including an expansion bump 131 surrounding thebar bump of the signal line 15 such that the space between the groundbump 13 and the bar bump of the signal line 15 is smaller than thatbetween the expansion bump 131 of the ground bump 13 and the terminal151 of the signal line 15. In the present embodiment, the expansion bump131 has an arc shape. Alternatively, the expansion bump 131 may alsohave other geometric shapes, such as but not limited to a square or adiamond shape.

Referring to FIG. 2B, a dielectric layer 17 is formed over the patternof high-frequency transmission structures and a portion of the substrate11. Next, a portion of the dielectric layer 17 is removed by using anywell known process, such as etching, to expose the terminal 151 and theexpansion bump 131. In one embodiment, the dielectric layer 17 may bemade of benzocyclobutene, photo-benzocyclobutene, polyimide, nitride,oxide or ceramic material.

As shown in FIG. 2C, a photoresist layer 19 is formed over thedielectric layer 17 and the substrate 11 by using any well knownprocess, such as spin coating or dry film covering process. Thephotoresist layer 19 is subjected to photolithography and etchingprocess to form a first pattern 191 and a second pattern 193. Theterminal 151 is exposed by the first pattern 191. The expansion bump 131and the portion of the dielectric layer 17 are exposed by the secondpattern 193. The exposed portion of the expansion bump 131 and theexposed portion of the dielectric layer 17 constitute a coaxial circularpattern with the terminal 151. It is understood that the shape of theexpansion bump 131 and the terminal 151 is not limited to be a circularpattern, the expansion bump 131 may also have other coaxial geometricshapes.

Next, an electroplating or an evaporation process is carried out to forma conductive layer over the first pattern 191 and the second pattern193, such as a titanium layer and then a gold layer thereon. The wholestructure is first subjected to a curing process and then thephotoresist layer 19 is removed to form a first conductive connector 201and a second conductive connector 203, a shown as FIG. 2D. The firstconductive connector 201 is electrically connected to the ground bump 13and electrically isolated from the signal line 15. The second conductiveconnector 203 is electrically connected to the terminal of the signalline 15 and electrically isolated from the ground bump 13. As shown inFIG. 2E, a substrate structure for high-frequency flip chip packageincludes the second conductive connector 203 serving as a centre of axisof the first conductive connector 201. The first and second conductiveconnectors 201 and 203 may be located over a central area of thesubstrate 11 Moreover, the signal line 15 of ground bump 13 located overthe edge of the substrate 11 is exposed for use for connection.

FIG. 3A is a top-view perspective diagram illustrating a high-frequencyflip chip package according to one embodiment of the present invention.As shown in FIG. 3A, the active surface (not shown in figure) of a chip29 is faced down. The circuit side of a packed chip 23 includes adielectric layer 27 thereon. The circuit side has the pattern ofhigh-frequency transmission structures similar to one shown in FIG. 2A,which includes a signal line 231 and a ground bump 23 around the signalline 231. Third conductive connectors 251 a and 251 b and fourthconductive connectors 253 a and 253 b are formed by using the sameprocess steps illustrated with reference to FIG. 2B to FIG. 2E. Thethird conductive connectors 251 a and 251 b respectively correspond toand disposed around the fourth conductive connectors 253 a and 253 b.The third conductive connectors 251 a and 251 b are electricallyconnected to the ground bump 23. One end of the fourth conductiveconnectors 253 a and 253 b respectively is electrically connected to thesignal line 231.

FIG. 3B is a scaled-up schematic diagram illustrating a transmissionstructure according to one embodiment of the present invention. Thedielectric layer is omitted for the convenience of illustration. Asshown in FIG. 3B, the signal line 15 and the ground bump 13 areseparately set over the substrate 11 and electrically isolated from eachother. Similarly, the ground bump 23 and the signal line 231 areseparately set over the chip and electrically isolated from each other.For forming the transmission structure, the signal line 15 over thesubstrate 11 is connected to the signal line 231 of the chip via thestructural connection of the second conductive connector (203 in FIG.2D) and the transmission of the fourth conductive connector 253 a/253 b.Accordingly, the application of the transmission structure to ahigh-frequency flip chip package may reduce the possibility of underfillfrom causing a vertical transmission between connected lines. Thus, thetransmission structure may enhance the transmission efficiency of amicrochip and a package substrate and further reduce both insertion loss(smaller than 0.6 dB) and return loss (smaller than 20 dB).

FIG. 4 is a schematic diagram illustrating the combination of asubstrate and a package according one embodiment of the presentinvention. The substrate 11 includes a first signal line 15 and a firstground bump 13 separately located and electrically isolated from eachother. The dielectric layer 17 covers a portion of the first ground bump13 and a portion of the first signal line 15. The flip chip 29 includesa second signal line 231 and a second ground bump 23 that are separatelylocated and electrically isolated from each other. The ring-shapedconductive connectors are located between the substrate and the flipchip, and electrically connected to the first ground bump 13 and thesecond ground bump 23. The second rod conductive connectors are locatedbetween the substrate and the flip chip, and structurally in contactwith the first signal line 15 and the second signal line 231. The secondrod conductive connector serves as a centre of axis of the firstring-shaped conductive connector. Accordingly, the vertical transmissionstructure may be applied, for example but not limited to, thetransmission between microstrip line and strip line, microstrip lines,coplanar waveguides, or coplanar waveguide and microstrip line.Moreover, the vertical transmission structure may be applied to the flipchip package, low temperature co-fired ceramics package (LTCC), hightemperature co-fired ceramics package (HTCC), organic laminate multichipmodules (MCM-L) or deposited thin film MCM (MCM-D).

Although the present invention has been explained in relation to itspreferred embodiment, it is to be understood that other modificationsand variation can be made without departing the spirit and scope of theinvention as hereafter claimed.

1. A transmission structure of high-frequency transmission line,comprising: a substrate, comprising an insulating surface; a pattern ofhigh-frequency transmission structures, formed over the insulatingsurface, comprising: a signal line, having a bar bump and a terminal;and a ground bump, electrically isolated from the signal line andsurrounding the terminal, comprising an expansion bump; a dielectriclayer, formed over the pattern of high-frequency transmissionstructures, wherein the dielectric layer exposes the terminal and theexpansion bump of the ground bump; a first conductive connector,disposed over the dielectric layer and in contact with the exposedexpansion bump; and a second conductive connector, disposed over thedielectric layer and in contact with the exposed terminal, wherein thesecond conductive connector serves as a centre of axis of the firstconductive connector.
 2. The transmission structure of high-frequencytransmission line according to claim 1, wherein a distance between theexpansion bump and the terminal is larger than a distance between theground bump and the bar bump.
 3. The transmission structure ofhigh-frequency transmission line according to claim 1, wherein thesubstrate comprises glass, silicon, ceramic or polymer.
 4. Thetransmission structure of high-frequency transmission line according toclaim 1, wherein the pattern of high-frequency transmission structurescomprises a copper layer or a gold layer.
 5. The transmission structureof high-frequency transmission line according to claim 1, wherein thefirst conductive connector and the second conductive connector comprisea titanium layer or a gold layer.
 6. The transmission structure ofhigh-frequency transmission line according to claim 1, wherein the firstconductive connector comprises a rod shape and the second conductiveconnector comprises a ring shape surrounding the first conductiveconnector.
 7. A transmission structure of a chip, comprising: a chip,having an insulating surface; a signal line, disposed over theinsulating surface, wherein the signal line includes a bar bump and twoterminals; a ground bump, electrically isolated from the signal line,comprising two expansion bumps respectively surrounding the twoterminal; a dielectric layer, disposed over the signal line and theground bump, wherein the dielectric layer exposes the two terminals anda portion of each expansion bump; two first conductive connectors,disposed over the dielectric layer, wherein the two first conductiveconnectors respectively correspond and in contact with the two exposedexpansion bumps; and two second conductive connectors, disposed over thedielectric layer and respectively in contact with the two exposedterminals, wherein each of the second conductive connectors respectivelyserves as a centre of axis of the first conductive connectors.
 8. Thetransmission structure of chip according to claim 7, wherein the secondsignal line and the ground bump comprise a copper layer or a gold layer.9. The transmission structure of chip according to claim 7, wherein thetwo first conductive connectors and the two conductive connectorscomprise a titanium layer or a gold layer.
 10. The transmissionstructure of chip according to claim 7, wherein each of the firstconductive connectors comprises a rod shape and each of the secondconductive connectors comprises a ring shape surrounding the firstconductive connector.
 11. A high-frequency flip chip package structure,comprising: a substrate, comprising a first signal line and a firstground bump separately set and electrically isolated from each other; aflip chip, comprising a second signal line and a second ground bumpseparately set and electrically isolated from each other; a firstconductive connector, located between the substrate and the flip chip,wherein the first conductive connector is electrically connected thefirst ground bump and the second ground bump; and a second conductiveconnector, located between the substrate and the flip chip, wherein thesecond conductive connector is connected to the first signal line andthe second signal line, and the second conductive connector serves as acentre of axis of the first conductive connector.
 12. The high-frequencyflip chip package structure according to claim 11, further comprising adielectric layer covering a portion of the first ground bump and aportion of the first signal line.
 13. The high-frequency flip chippackage structure according to claim 11, further comprising a dielectriclayer covering a portion of the second ground bump and a portion of thesecond signal line.
 14. The high-frequency flip chip package structureaccording to claims 12 or 13, wherein the dielectric layer comprises abenzocyclobutene, polyimide, nitride, oxide or ceramic layer.
 15. Thehigh-frequency flip chip package structure according to claim 11,wherein the substrate further comprises an insulating surface and ismade of glass, silicon, ceramic or polymer.
 16. The high-frequency flipchip package structure according to claim 11, wherein the firstconductive connector comprises a titanium layer or a gold layer.
 17. Thehigh-frequency flip chip package structure according to claim 11,wherein the second conductive connector comprises a titanium or goldlayer.
 18. The high-frequency flip chip package structure according toclaim 11, wherein the first ground bump and the first signal linecomprise a copper layer or a gold layer.
 19. The high-frequency flipchip package structure according to claim 11, wherein the second groundbump and the first signal comprise a copper or gold layer.